1. Field of the Invention
This invention relates to air bags and, more particularly, to an air bag cover assembly which operatively overlies an air bag and through which the air bag can be extended as the air bag is changed from an undeployed state by inflation thereof into a deployed state.
2. Background Art
Air bags are commonly used in automobiles to protect occupants from impact forces as in the event of a collision. The air bag is normally in a collapsed, undeployed state. In the event that the automobile is involved in a collision, the air bag inflates to a deployed state. A door on an instrument panel which operatively overlies the air bag is opened by the force developed by the air bag during the inflation so that the air bag can extend through the instrument panel into the passenger compartment of the vehicle to a protective position. In one form, the instrument panel is equipped with a door which is hinged at one side so that the entire dimension of the door pivots at the hinge region. This design is potentially dangerous in that a relatively large door could be thrust against a passenger during air bag deployment. In a worse case, the moving door could force the passenger""s head against a part of the vehicle, such as the front windshield thereon.
To address this problem, it is known to make the instrument panel door so that parts thereof open oppositely in a pivoting action. The smaller door parts represent less of a risk to the vehicle occupants upon deployment of the air bag.
It has also been a goal of designers of air bags to use a resin that has the ability to absorb shock upon impacting a rider. This minimizes the likelihood of injury resulting from deployment of the air bag.
Japanese Patent Laid-Open No. 129852/1999 is directed to an instrument panel over an air bag which is designed to address the above problems. The instrument panel consists of a core layer, a foamed layer, and a skin layer. The core layer has an opening through which the air bag extends as it is deployed. The core layer opening is closed by a door. The door is designed to absorb strain deformation caused by the difference in thermal expansion between the door and skin layer.
Upon deployment of the air bag, the door is repositioned and ruptures the foam layer and skin layer. As the air bag is deployed, the door has portions which pivot oppositely by reason of hinge parts which are formed by grooves in the door rearwardly of the core layer. As a result, the repositioning door is less likely to injure the vehicle occupants than if the door were made as a single pivoting piece. Further, the foamed material and skin layer are made with a resin material that has good shock absorbing properties. This also contributes to the safe operation of the overall system.
In the air bag system, such as that described above, there exists a risk that the air bag will not properly deploy under all environmental conditions. For safe operation, the air bag must be deployable reliably in both high and low temperature environments.
In the system disclosed in Japanese Patent Laid-Open No.129852/1999, the hinge structure is formed so that the thickness of the foamed layer between the hinge part and the skin layer is increased at the groove. With this construction, the foamed layer may inhibit inflation of the air bag. With the air bag inflated at low temperatures, the hinge part is prone to disconnecting, as a result of which the door may fully separate and become a dangerous projectile within the vehicle compartment.
While horizontal strain deformation for the skin layer and door may be absorbed by the foamed layer, deformation of the door under the force of the inflation of the air bag may not be absorbed. Accordingly, as shown in FIG. 9 herein, as expansion of the air bag 1 occurs in a low temperature environment, a tension may be applied to the skin layer 2 due to the deformation of the door parts 4, 5. This may cause generation of cracks 6 in the skin layer 2. This cracking occurs as the elastic limit of the skin layer is exceeded.
In a worse case, as the air bag of the type shown in Japanese Patent Laid-Open No.129852/1999 is expanded in a low temperature environment, the skin layer and door may fragment, with parts thereof being propelled potentially against the vehicle occupants. This may also inhibit proper expansion of the air bag.
Further, if the door cannot be consistently and reliably opened, the air bag may not properly inflate as a result of which the air bag does not afford the required protection to the occupants of a vehicle.
In one form, the invention is directed to an air bag cover assembly having a core layer, a cushioning layer, and a door. The core layer has an opening through which an air bag, which the air bag cover assembly operatively overlies, extends as the air bag is changed from an undeployed state into a deployed state. The skin layer has oppositely facing forward and rear surfaces and is situated forwardly of the core layer. The door is changeable between a closed state and an open state. In the closed state, the door covers the core layer opening. The door has a weakening portion which separates as an incident of the air bag changing from the undeployed state into the deployed state. The door has a first hinge with a curved portion which flexes to allow at least a first part of the door to pivot from a first position to a second position as an incident of the air bag changing from the undeployed state into the displayed state and the door changing from the closed state into the open state.
The weakening portion may consist of a groove.
In one form, the curved portion of the first hinge consists of a U-shaped forward surface and a U-shaped rear surface, each opening in a rear direction.
In one form, the curved portion of the first hinge has a thickness on the order of 1-2 mm.
In one form, the cushioning layer has a thickness between the curved portion of the first hinge and the skin layer on the order of 1-15 mm.
In one form, the door has a second part and a second hinge which flexes to allow the second part of the door to pivot from a third position to a fourth position as an incident of the air bag changing from the undeployed state into the deployed state.
The second hinge may have a curved portion which flexes as the second part of the door changes from the third position into the fourth position.
The curved portion of the second hinge may include a U-shaped forward surface and a U-shaped rear surface each opening in a rear direction.
The first and second door parts may pivot oppositely as the first door part moves from the first position into the second position and the second door part moves from the third position into the fourth position.
In one form, the groove has a V-shaped cross-sectional configuration.
The door may further include a forwardly projecting reinforcing rib.
In one form, the door has first and second reinforcing ribs and the groove resides between the first and second reinforcing ribs.
In one form, the skin layer has at least one groove therein at which the skin layer pivots as the door changes from the closed state into the open state.
The invention is also directed to an air bag cover assembly having a core layer, a skin layer, a cushioning layer, and a door. The core layer has an opening through which an air bag, which the air bag cover assembly operatively overlies, extends as the air bag is changed from an undeployed state into a deployed state. The skin layer has oppositely facing forward and rear surfaces and is situated forwardly of the core layer. The cushioning layer is between the core layer and the skin layer. The door is changeable between a closed state and an open state. The door in the closed state covers the core layer opening. The door has a weakening portion which separates as an incident of the air bag changing from the undeployed state into the deployed state. The door further has a first forwardly projecting reinforcing rib adjacent to the weakening portion.
In one form, the weakening portion has a groove and the door has a second forwardly projecting reinforcing rib with the groove residing between the first and second forwardly projecting reinforcing ribs.
In one form, the door has a first part that is pivotable from a first position into a second position as an incident of the air bag changing from the undeployed state into the deployed state and the door changing from the closed state into the open state.
In one form, the door has a second part that is pivotable from a third position into a fourth position as an incident of the air bag changing from the undeployed state into the deployed state and the door changing from the closed state into the open state.
In one form, the first door part has a reduced thickness portion defining a first hinge about which the first door part pivots in moving between the first and second positions.
The reduced thickness portion may have a curved shape.
In one form, the reduced thickness portion has a thickness on the order of 1-2 mm.
In one form, the cushioning layer has a thickness between the reduced thickness portion and a skin layer on the order of 1-15 mm.